The present invention relates to the field of downhole oil, gas, horizontal, and/or geothermal exploration and more particularly to the field of resistivity tools for tool strings employed in such exploration.
For the past several decades, engineers have worked to develop apparatus and methods to effectively obtain information about downhole formations, especially during the process of drilling. Logging-while-drilling (LWD) refers to a set of processes commonly used by the industry to obtain information about a formation during the drilling process in order to transmit the information from components located downhole on oil and gas drilling strings to the ground's surface. Various sensors and methods have been developed to obtain and transfer formation information to the surface. Due to the extreme conditions present in downhole environments, sensors must be used that can withstand great stresses.
Part of the difficulty comes from the fact that the operating environment can be extremely harsh, including temperatures as high as 200° C., pressures as high as 25,000 psi, and extremely abrasive and chemically corrosive conditions. Another source of difficulty comes from the fact that a drill string is made up of hundreds of components, such as sections of drill pipe and various downhole tools. Since these components are connected serially to create a drill string that may stretch for thousands of feet below the earth's surface, reliability is imperative. A failure in any essential downhole component can bring the whole system down and require an expensive “roundtrip” of the drill string to replace the defective component.
The prior art contains references to drill bits with sensors or other apparatus for data retrieval.
U.S. Pat. No. 6,814,162 to Moran, et al. which is incorporated by reference for all that it contains, discloses a drill bit, comprising a bit body, a sensor disposed in the bit body, a single journal removably mounted to the bit body, and a roller cone rotatably mounted to the single journal. The drill bit may also comprise a short-hop telemetry transmission device adapted to transmit data from the sensor to a measurement-while-drilling device located above the drill bit on the drill string.
U.S. Pat. No. 6,913,095 to Krueger, which is incorporated by reference for all that it contains, discloses a closed-loop drilling system that utilizes a bottom hole assembly (“BHA”) having a steering assembly having a rotating member and a non rotating sleeve disposed thereon. The sleeve has a plurality of expandable force application members that engage a borehole wall. A power source and associated electronics for energizing the force application members are located outside of the non rotating sleeve.
U.S. Pat. No. 5,138,263 to Towle, which is incorporated by reference for all that it contains, discloses a tool for evaluating electrical properties of an earth formation surrounding a borehole while drilling the borehole by electromagnetically coupling antennas with the formation.
U.S. Pat. No. 6,677,756 to Fanini, et al. which is incorporated by reference for all that it contains, discloses an induction tool for formation resistivity evaluations. The tool provides electromagnetic transmitters and sensors suitable for transmitting and receiving magnetic fields in radial directions.
U.S. Pat. No. 6,630,831 to Amini, which is incorporated by reference for all that it contains, discloses an invention that uses inductive magnetic coup ling of electromagnetic waves to EM barrier materials in combination with transmission of electromagnetic waves through non-permeable material to facilitate the measurement of resistivity of geologic formation beyond the well casing.
U.S. Pat. No. 6,577,129 to Thompson, et al. which is incorporated by reference for all that it contains, discloses an electromagnetic wave propagation resistivity borehole logging system comprising multiple groups of electromagnetic transmitter-receiver arrays operating at three frequencies.
U.S. Pat. No. 6,538,447 to Bittar, which is incorporated by reference for all that it contains, discloses a multi-mode resistivity tool for use in a logging-while-drilling system that includes an asymmetric transmitter design with multiple transmitters capable of generating electromagnetic signals at multiple depths of investigation.
U.S. Pat. No. 6,359,438 to Bittar, which is incorporated by reference for all that it contains, discloses a resistivity tool for use in an LWD system that includes a transmitter array with multiple transmitters positioned above a pair of receivers. The transmitters are selectively energized, causing current to be induced in the collar of the tool.
US Patent Application Publication No. 2006/0186888 to Wang, et al, which is incorporated by reference for all that it contain, discloses a measurement-while-drilling method and apparatus for determining the azimuth of providing magnetic field in a remote formation layer in the vicinity of a down hole resistivity tool. Coils are placed on the tool body having an external surface and a plurality of grooves are cut in the external surface of the tool body and oriented substantially horizontally with respect to the longitudinal axis of the tool body for the coils. Ferrite materials may be inserted in the grooves in between the coil wire and the bottom of the grooves.
U.S. Pat. No. 7,116,199 to Hall, et al, which is incorporated by reference for all that it contains, discloses an inductive coupler for downhole components. The inductive coupler includes an annular housing having a recess defined by a bottom portion and two opposing side wall portions. A plurality of generally U-shaped magnetically conductive electrically insulating segments, preferably comprised of ferrite, are disposed in the recess and aligned so as to form a circular trough.